It’s Probably a Bubble, but There Is Plenty Else to Invest In

Executive Summary

AI looks like a classic investment bubble to us, with very high valuations and signs of rampant speculation. But we recognize that while many investors harbor fears that AI might be a bubble, they are far from sure of that fact and tend to assume the market is appropriately priced as a fairly strong prior. In many bubbles, such a scenario would make building a strong portfolio close to impossible since the portfolio you’d hold if you believe in the bubble is a portfolio that would be crazy to hold if times were normal. The 2007-8 Everything Bubble and the 2021 Duration Bubble, for instance, were both bubbles in which the right portfolio to own if you believed there was a bubble was a portfolio that would have an unacceptably low expected return if markets were fairly priced. But the 2025 AI Bubble looks little like either of those two and much more like the 2000 Internet Bubble, in which a bubble-agnostic investor could have owned a portfolio with a reasonable risk/reward trade-off in either a bubble or a business-as-usual scenario. Today, non-U.S. equities, deep value stocks, and liquid alternatives offer returns that look reasonable or better, regardless of whether AI is in a bubble. Tilting a portfolio away from AI names and toward those assets may save investors a lot of pain if it turns out we are in a bubble without meaningfully reducing expected returns if financial markets are somehow still fairly priced today.

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Introduction

I think most people can admit that there may well be a bubble in AI and related stocks today. I won’t spend a lot of time discussing the evidence, but there is plenty to point to. The S&P 500 is trading at valuation levels only seen during the Internet Bubble, and on some measures, is even more expensive now than it was then. 1 Among other signs of rampant speculation, frantic venture capitalists are throwing money at AI startups at multi-billion-dollar valuations without even being told their plans.2 Equity investors are bidding up the value of giant companies by hundreds of billions of dollars due to investment deals with OpenAI, a company whose revenues would have to rise a hundredfold to make good on its promises. 3 Investors are so desperate to get in early on the next big thing that they’ve bid up the prices of quantum computing stocks 1200% or more over the past year, and at valuations that make Palantir look like a value stock. 4 It certainly looks like a bubble to us, although I don’t believe I’ll convince any true believers in the AI version of “this time it really is different” of that fact. 5 This letter is not written for the true believer, however. It is written instead for the “agnostic investor.” Such an investor is one who recognizes that there is plenty of evidence indicating we are in a bubble, but also harbors a belief that, despite that evidence, a decent starting assumption is that all assets are priced to deliver a normal return at all times. Bubbles are usually a problem for the agnostic investor, but some bubbles are more of a problem than others. The good news about today’s bubble is that it's one that allows an agnostic investor to build a portfolio that can strongly outperform if there is a bubble that ultimately bursts, and can also do just fine if all assets deliver normal returns.

A Taxonomy of Bubbles

One nice thing about 21st-century financial markets is that they’ve generated an interesting variety of bubbles well within the memory of most investors. When we made our case for the Internet Bubble in the late 1990s, our options were limited to the U.S. in 1929, the British Railway boom of the 1860s, and the Tulip Mania of the 1630s. 6 Outside of 1980s Japan, which had already been shrugged off as irrelevant to any “normal” country, the vast majority of investors hadn’t seen a meaningful investment bubble in their lifetimes. 7 But the last 25 years have given us three major bubbles in the developed world: the 2000 Internet Bubble, the 2007-8 Everything Bubble, and the 2021 Duration Bubble. Each of these bubbles varied significantly in terms of the assets involved and required investors to respond quite differently to protect their portfolios. Of them all, the current event looks most like the Internet Bubble of 2000, which should be a relief to the agnostic investor. While dynamic, valuation-driven asset allocation saved many investors considerable pain in all three bubbles, only in the 2000 event was it possible to spare yourself large losses without having to own a portfolio that would have been crazy to hold in any normal situation.

The Internet Bubble of 2000

The story of the Internet Bubble is familiar enough to most not to require a lot of retelling. The genuine breakthroughs in communications and computing that embodied the internet and (relatively) modern cell phone networks of the time sparked an investment frenzy where investors overestimated the rate of growth in communications traffic as well as the returns on investment for companies participating in the boom. Investors also did a poor and indiscriminate job of picking the eventual winners in the new economy that was being created. The S&P 500 rose to never-before-seen valuation levels, led by technology and telecommunications firms trading at unsustainably high valuations, sometimes with unsustainable business models as well. Vendor financing by suppliers and circular deals among internet firms created the illusion of greater activity and end-user demand than there actually was, and the S&P 500 ultimately fell by 45% in real terms from the summer of 2000 to the spring of 2003, while the tech-heavy Nasdaq Composite fell by 79%. It was a massive bubble that led to major pain for many investors, but that pain was largely avoidable, even for those without heroic prescience. To see why, it’s helpful to look at the height of the bubble through a valuation lens. Exhibit 1 shows a risk/reward scatterplot from June 2000 using the asset class forecasts we had published at the time. 8

Exhibit 1: Risk/Reward Trade-off in June 2000